ZF-2189: skipData processing
skipData information is stored within Lucene index. It's actually a "sub-index" of term documents list
Processing this info may help with a performance of some special query types.
If we process phrase query or multiterm query with several required terms and one term has very low selectivity (high cardinality), then we can process other terms first to limit result set. SkipData processing allows to avoid full document list scan for these high cardinality terms.
That makes sense in the case of huge indices (hundreds of thousands documents) and queries with terms having extremely low selectivity ('a', 'the', 'in', 'is', ...) StopWords analyzer may be used as workaround for this problem.